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  • Grinding on the lathe

    I needed to do a very small, light internal grinding job on the lathe. I could hold the part OK, but was having trouble figuring out how to spin the grinding wheel. I had an old 1/2hp 3450-rpm motor from a drill press, but that had no way to mount a small wheel on it, and it really didn't spin fast enough anyway.

    Looking around the shop for high-rpm motors, I spied a small trim router made for use with wood. It has a 1/4" collet to hold small router bits. I dug through my grinding stones and found one that would work, complete with 1/4" shank. It spins at up to 30k rpm. Now, I just had to mount the router somehow.

    I came up the a mounting as shown below, using all OEM edge guide accessories that came with the router. Add a couple of big G-clamps, and presto.


    It isn't a real robust, sturdy mount, but this particular job needs only a small amount of cleanup to finish the job. Others may want to keep this in mind for future small grinding jobs.
    If ignorance is bliss, why aren't there more happy people?

  • #2
    I think the problem you will see, as I saw when I tried something similar, is that the bearings in these things suck for applications like this. It will really effect your finish.

    Make sure you cover everything before doing any grinding. And it helps to have a vacuum near the wheel to help with the dust. Also dont forget you need to dress the stone with a diamond once it is mounted.

    And your mounting method is way to flimsy.

    Comment


    • #3
      2X on everything macona said. Keep in mind Rigid tools are Chinese so they do not have very good bearings.

      At one point I built a fixture to hold a Dayton electric die grinder for a similar set-up that did OK for its intended purpose. Not great, but OK.

      One other point is you need to make sure the wheel & the work are counter rotating (opposite directions).

      Comment


      • #4
        Thanks for all the warnings on things to watch out for. This setup worked fine for my particular task. As I said, it was a very light job.
        If ignorance is bliss, why aren't there more happy people?

        Comment


        • #5
          All the cautions are noted but if the finish and size are OK with the OP then it is OK.

          If it was a case of needing to grind it and if this was all that was available then he really only had two options - grind (which worked) it or leave it alone (which in the circumstances seemed to not be an option at all).

          For the OP: well thought out and well done.

          Comment


          • #6
            Originally posted by sbmathias
            I needed to do a very small, light internal grinding job on the lathe. I could hold the part OK, but was having trouble figuring out how to spin the grinding wheel. I had an old 1/2hp 3450-rpm motor from a drill press, but that had no way to mount a small wheel on it, and it really didn't spin fast enough anyway.

            Looking around the shop for high-rpm motors, I spied a small trim router made for use with wood. It has a 1/4" collet to hold small router bits. I dug through my grinding stones and found one that would work, complete with 1/4" shank. It spins at up to 30k rpm. Now, I just had to mount the router somehow.

            I came up the a mounting as shown below, using all OEM edge guide accessories that came with the router. Add a couple of big G-clamps, and presto.


            It isn't a real robust, sturdy mount, but this particular job needs only a small amount of cleanup to finish the job. Others may want to keep this in mind for future small grinding jobs.
            I can't see too much wrong with that set-up as it did the job it was intended to do.

            My guess is that the OP dressed the wheel (a lot of those "points" are quite well balanced) and if the wheel and the job were going in opposite directions at the point of contact it would be as good a finish as that set-up would allow - which was good enough for the OP.

            But if on the other hand the wheel and the job were moving in the same direction at the point of contact the wheel would have been "climb milling" and would tend to "climb and bounce" (giving a sort of "mottled" finish).

            For the OP: nice job.

            Comment


            • #7
              Nice job A dremel or rotozip work well also if you don't need a perfect finish.
              Craftsman 101.07403
              Grizzly G0704
              4x6 Bandsaw

              Comment


              • #8
                Originally posted by Dr Stan
                2X on everything macona said. Keep in mind Rigid tools are Chinese so they do not have very good bearings.

                At one point I built a fixture to hold a Dayton electric die grinder for a similar set-up that did OK for its intended purpose. Not great, but OK.

                One other point is you need to make sure the wheel & the work are counter rotating (opposite directions).
                Irrespective of where they are made, RIGID tools are still pretty good - as they'd have to in this instance in a high speed router.

                I'd like to see a documented support of your statement that "Keep in mind Rigid tools are Chinese so they do not have very good bearings" - if you have one. If you'd have said that there may be lesser quality bearing thanif/when Rigid was made in the USA I'd probably have accepted that - with reservations

                One other point is you need to make sure the wheel & the work are counter rotating (opposite directions).
                Nope.

                For external grinding they rotate in the same direction (similar to a lathe in "forward" drive) - this ensures that the wheel and the job points of contact direction are opposite to each other (ie the wheel point of contact - at the front of the wheel - is moving downwards and the work point of contact - at the back/rear of the work - is moving upwards which is why the sparks and coolant are ejected downwards - by the wheel.

                In the case of internal grinding the wheel and the job rotate in the same direction so that as before the direction of the wheel and the job are opposite each other at the (grinding) point of contact.

                Care may be needed to consider heat due to grinding, the more so if no coolant is used.

                The wheel should be dressed initially and kept dressed to keep it sharp.

                It is often best if the wheel is dressed to only have a small "land" in contact with the job.

                "Climb" grinding is generally a no-no but can be used with caution.
                Last edited by oldtiffie; 07-19-2012, 07:44 PM.

                Comment


                • #9
                  If one where to look at the set up from the tailstock the work would be rotating counterclockwise (forward). The wheel in this case should be rotating clockwise otherwise the wheel would effectively be skipping on the work surface. This is the way we always performed cylindrical grinding (OD & ID) when I was in industry.

                  Comment


                  • #10
                    I made a special bracket for mounting a Zip tool to my QCTP for grinding. The Zip tool was fairly new and, in fact, it had never been used for anything arduous before. It worked fine for the first few jobs and I was able to obtain tolerable finishes on hard materials (A2 RC60.) But the bearing went to hell after a student used the setup to part off and groove a bent automobile axle using an abrasive cutoff wheel. The Zip tool was made in the USA. I have no idea where the bearings were made.

                    -DU-

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                    • #11
                      Looks better than a Dremel, electrical tape, and a 8" piece of Unistrut on the toolpost that I used to grind a reamer once!!

                      Comment


                      • #12
                        I find it as funny as hell when someone shows how he successfully completed a job and a few SAE's jump in to tell him that what he did couldn't possibly work.

                        Comment


                        • #13
                          Originally posted by cameron View Post
                          I find it as funny as hell when someone shows how he successfully completed a job and a few SAE's jump in to tell him that what he did couldn't possibly work.
                          "successfully completed a job" doesn't mean much. We don't even have the vaguest idea what the job was and no idea how it turned out , other than "successsful". What is "successful"? Is it +/- .010? Is it a 125 finish or is it single digits?
                          Thomas Edison was successful with the incandescent light. But by his own account he failed thousands of times in the effort. So how successful was he? If the purpose of a home shop is to piddle away time on a hobby then failure= time piddled= success.
                          The facts are that the lathe is not made more accurate because someone cobbled up a half ass grinding arrangement or even a proper tool post grinder. It has the same ways and spindle bearings as before. If anything, accuracy is less, because the grinding appliance with, to be generous, bearings of unknown quality has been introduced.
                          There are basically 2 reasons for grinding, size and finish. Introducing a grinding machine of questionable quality will not improve a lathe's capability in either. With a properly ground boring bar the OP could have held size and finish better without the grinder in most materials. If the material must be ground, not machinable by other means, then he did what he had to do., Until we know what the job was and what "successful" means then this does not look like a good idea.

                          Comment


                          • #14
                            oldtiffie-

                            Are you the chap with 3 or 4 newish Chinese cutter grinders in your shop?
                            I would have thought you would set up your job on one of those.

                            --Doozer
                            DZER

                            Comment


                            • #15
                              Originally posted by tdmidget View Post
                              "successfully completed a job" doesn't mean much. We don't even have the vaguest idea what the job was and no idea how it turned out , other than "successsful". What is "successful"? Is it +/- .010? Is it a 125 finish or is it single digits?
                              Thomas Edison was successful with the incandescent light. But by his own account he failed thousands of times in the effort. So how successful was he? If the purpose of a home shop is to piddle away time on a hobby then failure= time piddled= success.
                              The facts are that the lathe is not made more accurate because someone cobbled up a half ass grinding arrangement or even a proper tool post grinder. It has the same ways and spindle bearings as before. If anything, accuracy is less, because the grinding appliance with, to be generous, bearings of unknown quality has been introduced.
                              There are basically 2 reasons for grinding, size and finish. Introducing a grinding machine of questionable quality will not improve a lathe's capability in either. With a properly ground boring bar the OP could have held size and finish better without the grinder in most materials. If the material must be ground, not machinable by other means, then he did what he had to do., Until we know what the job was and what "successful" means then this does not look like a good idea.
                              For this job, I had to deepen the bore on a hardened sleeve by cutting back the internal shoulder by just a few thousandths. I tried cutting it with a brazed carbide, but it was too hard for that. I saw no other way to do it except by grinding. I had to go slowly, and use coolant judiciously, but in the end it worked well, with a good finish.
                              I admit that this is not using the router in its intended way, but it seems like its bearings should be able to cut many linear feet of hard wood with a carbide router bit, and still function correctly. Part of using any tools is to have a sense for how robust the setup and tools are, and push them no harder than they can stand and still do their job. I believe I did that with this setup. Half-assed? Maybe. Successful? Yes.
                              If ignorance is bliss, why aren't there more happy people?

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